Vertical transistor and method for fabricating the same

ABSTRACT

Various embodiments of the present invention disclosure are directed to a vertical transistor having different doping profiles in its upper channel layer and lower channel layer for reducing leakage current while enhancing contact resistance and a method for manufacturing the vertical transistor.According to an embodiment of the present invention disclosure, a semiconductor device comprises a lower contact, a vertical channel layer on the lower contact, the vertical channel layer including a metal component and an oxygen component, and an upper contact on the vertical channel layer. The vertical channel layer has a gradual doping profile in which a doping concentration of the metal component is lowest in an intermediate region and gradually increases from the intermediate region to the upper contact.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application No.10-2021-0003864, filed on Jan. 12, 2021, which is herein incorporated byreference in its entirety.

BACKGROUND 1. Field

The present invention disclosure relates to a vertical transistor and amethod of manufacturing the same, and, more specifically, to a verticaltransistor using an oxide semiconductor as a channel layer and a methodof manufacturing the same.

2. Description of the Related Art

As memory devices are highly integrated, technologies for applyingvertical transistors have been proposed to increase the density oftransistors. Technologies for applying an oxide semiconductor havingexcellent electrical characteristics as a channel material for verticaltransistors have also been proposed.

SUMMARY

Various embodiments of the present invention disclosure are directed toa vertical transistor having different doping profiles in its upperchannel layer and lower channel layer for reducing leakage current whileenhancing contact resistance and a method for manufacturing the verticaltransistor.

According to an embodiment of the present invention disclosure, asemiconductor device comprises a lower contact, a vertical channel layeron the lower contact, the vertical channel layer including a metalcomponent and an oxygen component, and an upper contact on the verticalchannel layer. The vertical channel layer has a gradual doping profilein which a doping concentration of the metal component is lowest in anintermediate region and gradually increases from the intermediate regionto the upper contact.

According to an embodiment of the present invention disclosure, avertical transistor comprises a lower contact on a substrate, is achannel layer including a lower channel layer, an intermediate channellayer, and an upper channel layer sequentially formed on the lowercontact, the channel layer including a metal component and an oxygencomponent, and an upper contact on the upper channel layer. The channellayer has a gradual doping profile in which a doping concentration ofthe metal component is lowest in the intermediate channel layer and, inthe upper channel layer, gradually increases towards the upper contact.

According to an embodiment of the present invention disclosure, a methodfor manufacturing a vertical transistor comprises forming a lowercontact material on a substrate, forming a lower channel materialincluding a metal component and an oxygen component on the lower contactmaterial, forming a channel material including a metal component and anoxygen component on the lower channel material, and performing atreatment on the channel material to separate the channel material intoan intermediate channel material and an upper channel material on theintermediate channel material.

According to an embodiment of the present invention disclosure, leakagecurrent may be reduced by forming different doping profiles in the upperchannel layer and the lower channel layer.

According to an embodiment of the present invention disclosure, contactresistance may be enhanced by forming a upper insertion layer betweenthe channel layer and the upper contact and a lower insertion layerbetween the channel layer and the lower contact.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a vertical transistoraccording to an embodiment;

FIG. 2 is a perspective view illustrating an upper contact, lowercontact, and channel layer of a vertical transistor according to anembodiment;

FIGS. 3A, 3C, 3D, 3E, 3F, 3G, 3H, and 3I are views illustrating anexample method for manufacturing a vertical transistor according to anembodiment;

FIGS. 4A, 4B, 4C, and 4D are perspective views illustrating an uppercontact, lower contact, and channel layer of a vertical transistoraccording to an embodiment;

FIG. 5 is a perspective view illustrating a vertical transistoraccording to an embodiment;

FIG. 6 is a perspective view illustrating an upper contact, lowercontact, and channel layer of a vertical transistor according to anembodiment;

FIGS. 7A and 7B are perspective views illustrating an upper contact,lower contact, and channel layer of a vertical transistor according toan embodiment; and

FIG. 8 is a perspective view illustrating a vertical transistoraccording to an embodiment.

DETAILED DESCRIPTION

Example cross-sectional views, plan views, and block diagrams may beused herein to describe various embodiments of the disclosure, andmodifications may be made thereto according to, e.g., manufacturingtechniques and/or tolerances. Thus, embodiments of the disclosure arenot limited to specific types as shown and illustrated herein but mayrather encompass changes or modifications resultant from fabricatingprocesses. For example, the regions or areas shown in the drawings maybe schematically shown, and their shapes shown are provided merely asexamples, rather as limiting the category or scope of the disclosure.Elements shown in the drawings may be exaggerated in light of theirthicknesses and intervals for illustration purposes. Well knowncomponents or elements irrelevant to the subject matter of thedisclosure may be omitted from the description. The same or ssubstantially the same reference denotations are used to refer to thesame or substantially the same elements throughout the specification andthe drawings. Hereinafter, embodiments of the disclosure are describedin detail with reference to the accompanying drawings.

FIG. 1 is a perspective view illustrating a vertical transistoraccording to an embodiment.

As illustrated in FIG. 1, a vertical transistor 100 may include a stackstructure including a lower contact 110, a channel layer 120, and anupper contact 130. The vertical transistor 100 may further include adielectric layer 140 and gate 150 formed on a side surface of thechannel layer 120. That is, the lower contact 110, the channel layer120, and the upper contact 130 may have a stack structure in a directionextending perpendicular to a substrate (not shown), while the dielectriclayer 140 and the gate 150 may have a stack structure in a directionextending parallel to the substrate (not shown).

The lower contact 110 and the channel layer 120 may have a square columnshape, however, the shape of the lower contact 110 and the channel layer120 may not be limited thereto, and may include various other shapes(e.g., a rectangular column shape or a cylindrical shape), as may beneeded. The lower contact 110 and the channel layer 120 may have thesame width. The upper contact 130 may have a cylindrical shape, however,the shape of the upper contact 130 may not be limited thereto, and mayinclude various other shapes (e.g, a square column shape or arectangular column shape), as may be needed.

The diameter (or width when the upper contact 130 has a square columnshape) of the upper contact 130 may be smaller than the diameter (orwidth) of the channel layer 120. The dielectric layer 140 may be formedon a side surface of the channel layer 120. The dielectric layer 140 maycover all sidewalls of the channel layer 120. That is, the dielectriclayer 140 may be formed to surround the entire side surface of thechannel layer 120. The channel layer 120 and the dielectric layer 140may have the same height. Height refers to the dimension of the channellayer 120 and dielectric layer 140 in the direction in which they arestacked. The gate 150 may be formed to surround the dielectric layer140. The thickness of the gate 150 may be larger than the thickness ofthe dielectric layer 140. The gate 150 may cover all sidewalls of thedielectric layer 140. That is, the gate 150 may be formed to surroundthe entire side surface of the dielectric layer 140. Accordingly, thedielectric layer 140 may be positioned between the gate 150 and thechannel layer 120.

The lower contact 110 may be disposed on the substrate, for example, asemiconductor substrate (not shown). The lower contact 110 may include ametal-containing material. The lower contact 110 may include a metal ora metal compound. The lower contact 110 may include atungsten-containing material. Alternatively, the lower contact 110 mayinclude a semiconductor material. The lower contact 110 may include asilicon-containing material. The lower contact 110 may be doped with animpurity.

The channel layer 120 may he positioned on the lower contact 110. Thechannel layer 120 may be referred to as a ‘vertical channel layer’. Thechannel layer 120 may include an oxide. The channel layer 120 mayinclude a metal component and an oxygen component. The channel layer 120may include an oxide semiconductor. For example, the channel layer 120may include at least one of indium (In), gallium (Ga), or zinc (Zn). Thechannel layer 120 may include InSn, InGaZnO, InSnZnO, InGASnO, InSnO,InZnO, InGaO, or a combination thereof. The channel layer 120 may bedoped with an impurity. The channel layer 120 may be doped with silicon(Si) or germanium (Ge). The doping profile of the metal materialaccording to the height of the channel layer 120 may not be uniform. Anexample of a doping profile is described below.

The upper contact 130 may be positioned on the channel layer 120. Theupper contact 130 may include the same material as the lower contact110. In another embodiment, the upper contact 130 may include adifferent material from that of the lower contact 110. The upper contact130 may include a metal-containing material. The upper contact 130 mayinclude a metal or a metal compound. The upper contact 130 may include atungsten-containing material. Alternatively, the upper contact 130 mayinclude a semiconductor material. The upper contact 130 may include asilicon-containing material. The upper contact 130 may be doped with animpurity. Any suitable impurity may be used.

The vertical transistor 100 may include the gate 150 surrounding thesidewalls of the channel layer 120 while sharing the same axis. Thedielectric layer 140 may be positioned between the gate 150 and thechannel layer 120. The gate 150 may be spaced apart from the channellayer 120 by the dielectric layer 140. The gate 150 may include a metalor a metal compound. The dielectric layer 140 may be any suitabledielectric layer known in the art. According to an embodiment, thedielectric layer 140 may include a high-k material, such as HfO₂, ZrO₂or other metal oxides.

FIG. 2 is a perspective view illustrating an upper contact, lowercontact, and channel layer of a vertical transistor according to anembodiment. FIG. 2 is a view in which the dielectric layer 140 and gate150 of FIG. 1 are omitted to describe the channel layer 120 of FIG. 1.

As illustrated in FIG. 2, the channel layer 120 may include a lowerchannel layer 121 formed on the lower contact 110, an intermediatechannel layer 122 formed on the lower channel layer 121, and an upperchannel layer 123 formed on the intermediate channel layer 122. That is,the channel layer 120 may include a stack of the lower channel layer121, the intermediate channel layer 122, and the upper channel layer123. The height LBO of the lower channel layer 121, the height LG of theintermediate channel layer 122, and the height LTO of the upper channellayer 123 may be the same or different.

The channel layer 120 may include an oxide. The channel layer 120 mayinclude a metal material and an oxygen material. The channel layer 120may include an oxide semiconductor. The channel layer 120 may be dopedwith an impurity. In the channel layer 120, the doping profile ofimpurities according to the height may not be uniform. The dopingprofiles of impurities may be different in the lower channel layer 121,the intermediate channel layer 122, and the upper channel layer 123,respectively.

The graph of FIG. 2 illustrates the doping concentration of the metalcomponent as a function of a height position. Metailicity may increaseas the doping concentration increases. As the metallicity of the uppersurface of the channel layer 120 increases, the contact resistance tothe upper contact 130 may decrease. As the metallicity of the lowersurface of the channel layer 120 increases, the contact resistance tothe lower contact 110 may decrease.

The channel layer 120 may have a gradual doping profile in which thedoping concentration of the metal component gradually increases in theregion closer to the upper contact 130, e.g., as going closer to theupper contact 130 from the boundary between the intermediate channellayer 122 and the upper channel layer 123. The channel layer 120 mayhave an abrupt doping profile in which the doping concentration of themetal component abruptly varies in the region closer to the lowercontact 110, e.g., at the boundary between the intermediate channellayer 122 and the lower channel layer 121. That is, at the boundarybetween the intermediate channel layer 122 and the lower channel layer121, the doping concentration of the metal component may increaserapidly. For example, the abrupt doping profile may include a stepchange profile.

The doping concentration may be divided into a first doping region P1according to the height LB of the lower contact, a second doping regionP2 according to the height LBO of the lower channel layer, a thirddoping region P3 according to the height LG of the intermediate channellayer, a fourth doping region P4 according to the height LTO of theupper channel layer, and a fifth doping region P5 according to theheight LT of the upper contact. The doping concentration of the first tofifth doping regions P1 to P5 may be continuous. The dopingconcentration in the instant embodiment refers to the dopingconcentration of the metal component.

First, the doping concentrations of the first doping region P1, thesecond doping region P2, and the third doping region P3 may each includea constant value. That is, in the lower contact 110, the lower channellayer 121, and the intermediate channel layer 122, the dopingconcentration of the metal component doped in the film may be uniformlymaintained. The doping profiles of the first doping region P1, thesecond doping region P2, and the third doping region P3 may include astepped profile. The doping concentration of the first doping region P1may be greater than the doping concentration of the second doping regionP2 and the third doping region P3. The doping concentration of thesecond doping region P2 may be greater than the doping concentration ofthe third doping region P3. The third doping region P3 may include thelowest doping concentration among the first to fifth doping regions P1to P5. The difference in doping concentration between the second dopingregion P2 and the third doping region P3 may be greater than thedifference in doping concentration between the first doping region P1and the second doping region P2. The difference in doping concentrationbetween the second doping region P2 and the third doping region P3 maybe at least two times greater than the difference in dopingconcentration between the first doping region P1 and the second dopingregion P2. That is, there may be provided an abrupt doping profile inwhich at the boundary between the third doping region P3 and the seconddoping region P2, the doping concentration of the metal componentrapidly increases from the third doping region P3 to the second dopingregion P2. As the difference in doping concentration between the thirddoping region P3 and the second doping region P2 increases, thedifference in doping concentration between the second doping region P2and the first doping region P1 may decrease. As the difference in dopingconcentration between the second doping region P2 and the first dopingregion Pt decreases, the contact resistance to the lower contact 110 maydecrease.

The doping concentration of the fourth doping region P4 may increasewith a constant slope in a direction from the fourth doping region P4 tothe fifth doping region P5. The doping concentration of the fourthdoping region P4 may increase from a doping concentration equal to thedoping concentration of the third doping region P3 to a dopingconcentration equal to the doping concentration of the fifth dopingregion P5. The doping concentration of the fourth doping region P4 mayincrease from a doping concentration equal to the doping concentrationof the third doping region P3 to a doping concentration equal to thedoping concentration of the second doping region P2. That is, the fourthdoping region P4 may include a gradual doping profile in which thedoping concentration of the metal component gradually increases as itapproaches the upper surface of the upper channel layer 123.

In another embodiment, the doping profile of the fourth doping region P4may have an increased slope of the doping concentration according to theheight. In another embodiment, the doping profile of the fourth dopingregion P4 may have a reduced slope. As the fourth doping region P4 has agradual doping profile, leakage current may be reduced. As thedifference in doping concentration between the fourth doping region P4and the fifth doping region P5 decreases, the contact resistance to theupper contact 130 may decrease.

The doping concentration of the fifth doping region P5 may have aconstant value. The doping concentration of the fifth doping region P5may be lower than or equal to the doping concentration of the firstdoping region P1. The doping concentration of the fifth doping region P5may be continuous from the doping concentration of the fourth dopingregion P4.

According to the present embodiment, the leakage current of the verticaltransistor 100 may be reduced by varying the doping profile ofimpurities as a function of the height. According to the presentembodiment, the contact resistance to the lower contact 110 and theupper contact 130 may be reduced by forming a higher dopingconcentration at the upper and lower surfaces of the channel layer 120.

FIGS. 3A to 3I are views illustrating a method of manufacturing avertical transistor according to an embodiment.

Referring to FIG. 3A, a substrate 11 may be prepared. The is substrate11 may include a semiconductor substrate. The substrate 11 may be formedof a silicon-containing material. The substrate 11 may include othersemiconductor material, e.g., germanium. The substrate 11 may include aIII-V group semiconductor substrate. The substrate 11 may include acompound semiconductor substrate, such as GaAs. The substrate 11 mayinclude a silicon-on-insulator (SOI) substrate.

A lower contact material 12A may be formed on the substrate 11. Thelower contact material 12A may include a metal-containing material. Thelower contact material 12A may include a metal or a metal compound. Thelower contact material 12A may include a tungsten-containing material.The lower contact material 12A may be doped with an impurity. In anotherembodiment, the lower contact material 12A may include asilicon-containing material. The lower contact material 12A may includepolysilicon. The lower contact material 12A may include impurity-dopedpolysilicon.

A lower channel material 13A may be formed on the lower contact material12A. The thickness of the lower channel material 13A may be smaller thanthe thickness of the lower contact material 12A. The lower channelmaterial 13A may include an oxide. The lower channel material 13A mayinclude a metal component and an oxygen component. The lower channelmaterial 13A may include an oxide semiconductor. For example, the lowerchannel material 13A may include at least one of indium (In), gallium(Ga), or zinc (Zn). The lower channel material 13A may include InSn,InGaZnO, InSnZnO, InGASnO, InSnO, InZnO, InGaO, or a combinationthereof. The lower channel material 13A may be doped with an impurity.For example, the lower channel material 13A may be doped with silicon(Si) or germanium (Ge).

The lower channel material 13A may be deposited in an oxygen atmosphere.The lower channel material 13A may be deposited in a low-concentrationoxygen atmosphere (O₂ Ambient). Accordingly, oxygen deficiency isincreased, thereby forming a film with a high doping concentration ofmetal component. The lower channel material 13A may include a dopingprofile having a constant doping concentration. The doping concentrationof the lower channel material 13A may be the same or different (e.g.,lower) than the doping concentration of the lower contact material 12A.

The lower channel material 13A may be formed by a method, such aschemical vapor deposition (CVD), physical vapor deposition (PVD), atomiclayer deposition (ALD), plasma enhanced CVD (PECVD), or plasma enhancedALD (PEALD). The lower channel material 13A may be deposited at roomtemperature. Deposition at room temperature may prevent oxygendiffusion.

A channel material 14 may be formed on the lower channel material 13A.The thickness of the channel material 14 may be larger than thethickness of the lower channel material 13A.

The channel material 14 may include the same material as the material ofthe lower channel material 13A. The channel material 14 may include anoxide. The channel material 14 may contain a metal component and anoxygen component. The channel material 14 may include an oxidesemiconductor. For example, the channel material 14 may include at leastone of indium (In), gallium (Ga), or zinc (Zn). The channel material 14may include InSn, InGaZnO, InSnZnO, InGASnO, InSnO, InZnO, InGaO, or acombination thereof. The channel material 14 may be doped withimpurities. For example, the channel layer 120 may be doped with silicon(Si) or germanium (Ge).

The channel material 14 may be deposited in an oxygen atmosphere. Thechannel material 14 may be deposited in a high-concentration oxygenatmosphere (O₂ Ambient). Accordingly, oxygen deficiency is reduced,thereby forming a film with a low doping concentration of metalcomponent. The channel material 14 may include a doping profile having aconstant doping concentration. The doping concentration of the metalcomponent of the channel material 14 may be smaller than the dopingconcentration of the lower channel material 13A. At the boundary betweenthe lower channel material 13A and the channel material 14, the dopingconcentration of the metal component may abruptly change. Accordingly,an abrupt doping profile may be formed in which at the boundary betweenthe lower channel material 13A and the channel material 14, the dopingconcentration of the metal component rapidly changes.

The channel material 14 may be formed by a method, such as chemicalvapor deposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), plasma enhanced CVD (PECVD), or is plasma enhanced ALD(PEALD). The channel material 14 may be deposited at room temperature.Deposition at room temperature may prevent oxygen diffusion.

The lower channel material 13A and the channel material 14 may be formedex-situ in their respective devices, or may be formed in-situ in onedevice.

As illustrated in FIG. 3B, the channel material 14 may be separated intoan intermediate channel material 15A and an upper channel material 16A.The intermediate channel material 15A and the upper channel material 16Amay be divided according to doping profiles. The step of separating thechannel material 14 into the intermediate channel material 15A and theupper channel material 16A may be performed in-situ with the step offorming the channel material 14.

To separate the channel material 14 into the intermediate s channelmaterial 15A and the upper channel material 16A, a treatment may beperformed. As the treatment is performed, the doping profile accordingto the height of the channel material 14 may be adjusted. As thetreatment is performed, oxygen deficiency may be formed in the channelmaterial 14. Oxygen deficiency may be formed to increase toward an upperlevel of the channel material. Accordingly, the channel material 14 maybe divided into the intermediate channel material 15A having a constantdoping concentration of the metal material and the upper channelmaterial 16A having a doping concentration of the metal materialgradually increasing toward the upper surface of the channel is material14. The doping concentration of the intermediate channel material 15Amay be the same as the doping concentration at the time of deposition ofthe channel material 14. The intermediate channel material 15A mayinclude a constant doping profile. The upper channel material 16A mayinclude a doping profile that increases with a constant slope from thedoping concentration of the intermediate channel material 15A. Inanother embodiment, the doping profile of the upper channel material 16Amay include a slope that is not constant. The upper channel material 16Amay include a gradual doping profile in which the doping concentrationof the metal component gradually increases as it approaches the uppersurface.

The treatment may include use of plasma. For example, plasma treatmentenergy may be adjusted to form oxygen deficiency. The plasma treatmentenergy may increase from an upper level to a lower level of the upperchannel material 16A.

The treatment may include use of ions. For example, the ions may includeinert gases, such as He, Ne, Ar, Kr, Xe, or a combination thereof whichmay be used to perform the treatment. Both plasma and ions may be usedto form oxygen deficiency. The treatment using both plasma and ions maybe referred to as ‘multi plasma treatment’. When performing the‘multi-plasma treatment’, a higher doping concentration may be formed atthe upper surface of the upper channel material 16A.

Accordingly, the doping profile of the metal material according to theheight of FIG. 3B may be the same as the doping profile of the first tofourth doping regions P1 to P4 illustrated in FIG. 2A.

As illustrated in FIG. 3C, the upper channel material 16A, theintermediate channel material 15A, the lower channel material 13A, andthe lower contact material 12A may be etched, thereby forming the upperchannel layer 16, the intermediate channel layer 15, the lower channellayer 13, and the lower contact 12, respectively. The upper channellayer 15, the intermediate channel layer 15, and the lower channel layer13 may constitute a channel layer CH.

The upper channel material 16A, the intermediate channel material 15A,the lower channel material 13A, and the lower contact material 12A maybe etched using a first mask (not shown) as an etching mask.Accordingly, the upper channel layer 16, the intermediate channel layer15, the lower channel layer 13, and the lower contact 12 may have thesame width. The channel layer CH and the lower contact 12 may have arectangular column shape. In another embodiment, the channel layer CHand the lower contact 12 may have a different shape (e.g., a cylindricalshape).

As illustrated in FIG. 3D, an upper contact material 17A covering thechannel layer CH and the lower contact 12 may be formed. The uppercontact material 17A may also cover the surface of the substrate 11.

The upper contact material 17A may include the same material as thelower contact 12. The upper contact material 17A may include ametal-containing material. The upper contact material 17A may include ametal or a metal compound. The upper contact material 17A may include atungsten-containing material. The upper contact material 17A may bedoped with impurities. In another embodiment, the upper contact material17A may include a silicon-containing material. The upper contactmaterial 17A may include polysilicon. The upper contact material 17A mayinclude polysilicon doped with impurities.

As illustrated in FIG. 3E, an upper contact 17 may be formed on thechannel layer CH.

The upper contact material 17A may be etched to form the upper contact17 using a second mask (not shown) as an etching mask. The upper contact17 may have a cylindrical shape. The diameter (or width) of the uppercontact 17 may be smaller than the diameter (or width) of the channellayer CH. The height of the upper contact 17 may be the same as ordifferent from the height of the lower contact 12.

In another embodiment, when forming the upper contact 17, the channellayer CH and the lower contact 12 may be formed together. In this case,the upper contact 17, the channel layer CH, and the lower contact 12 mayhave the same width. The upper contact 17, the channel layer CH, and thelower contact 12 may have a cylindrical shape. In another embodiment,the upper contact 17, the channel layer CH, and the lower contact 12 mayall have a rectangular column shape.

As illustrated in FIG. 3F, an insulation layer 18 covering sidewalls ofthe lower contact 12 may be formed.

To form the insulation layer 18, after forming an insulation material18A covering all of the upper contact 17, the channel layer CH, thelower contact 12, and the surface of the substrate 11, the insulationmaterial 18A may be removed to have the same height as the lower contact12. To remove the insulation material 18A, a process, such as etchback,may be performed. Accordingly, the height of the insulation layer 18 maybe the same as the height of the lower contact 12. The insulation layer12 may include oxide, nitride, or a combination thereof.

As illustrated in FIG. 3G, a dielectric material 19A may be formed tocover exposed surfaces of the insulation layer 18, the channel layer CH,and the upper contact 17. The dielectric material 19A may be conformallyformed along the exposed surfaces of the insulation layer 18, thechannel layer CH and the upper contact 17. The dielectric material 19Amay be any dielectric material known in the art. The dielectric material19A according to an embodiment may include a high-k material, such asHfO₂, ZrO₂, or other metal oxide.

As illustrated in FIG. 3H, the dielectric material 19A may be partiallyremoved to remain only on the sidewall of the channel layer CH. Thus,the dielectric layer 19 may be formed.

The dielectric layer 19 may cover all the exposed sidewalls of thechannel layer CH, i.e, the sidewalls of the channel layer CH which arenot covered by the insulation layer 18. The height of the dielectriclayer 19 may be the same as the height of the channel layer CH. Thedielectric layer 19 may be conformally formed on the channel layer CH.In another embodiment, the dielectric layer 19 may cover only some ofthe exposed sidewalls of the channel layer CH, for example, a pair ofdielectric layers 19 parallel to each other may be formed on bothopposite exposed sidewalls of the channel layer CH.

As illustrated in FIG. 31, a gate 20 covering the exposed surface of thedielectric layer 19 may be formed on the insulation layer 18. To formthe gate 20, a gate material 20A may be formed first and then may bepartially removed to form the gate 20 having the same height as thedielectric layer 19. Accordingly, the height of the gate 20 may be thesame as the height of the channel layer CH. The dielectric layer 19 maybe positioned between the gate 20 and the channel layer CH. The gate 20may cover the upper surface of the insulation layer 18. The gate 20 mayinclude a metal or a metal compound.

The vertical transistor formed according to the present manufacturingmethod may reduce leakage current by having different dopingconcentrations of the metal component according to a height position inthe channel layer CH.

In the vertical transistor formed according to the present manufacturingmethod, the doping concentration at the upper surface of the channellayer CH is dose to that of the upper contact 17, and the dopingconcentration at the lower surface of the channel layer CH is dose tothat of the lower contact 12 so that the contact resistance may beenhanced.

FIGS. 4A to 4D are perspective views illustrating examples of verticaltransistors. FIGS. 4A to 4D are views in which the dielectric layer 140and the gate 150 of FIG. 1 are omitted to describe the lower contact110, the channel layer 120, and the upper contact 130 according tovarious embodiments. Accordingly, the vertical transistors 101, 102,103, and 104 of FIGS. 4A to 4D may be similar to each other. Thevertical transistors 101, 102, 103, and 104 of FIGS. 4A to 4D may besimilar to the vertical transistor 100 of FIG. 2. Accordingly, the samereference denotations as those in FIG. 2 among the reference denotationsof FIGS. 4A to 4D may refer to the same components. Descriptions ofduplicate components may be omitted or briefly described.

First, as illustrated in FIG. 4A, a vertical transistor 101 may beformed. The vertical transistor 101 may include a upper insertion layer124 on the upper channel layer 123.

The upper insertion layer 124 may have a cylindrical shape. The upperinsertion layer 124 may have the same diameter (or width) as the uppercontact 130. The upper insertion layer 124 may overlap the bottomsurface of the upper contact 130. The upper insertion layer 124 maypartially cover the upper surface of the upper channel layer 123.

The upper insertion layer 124 may be formed of an indium (In) or anindium-tin (InSn) compound. The upper insertion layer 124 may be formedby physical vapor deposition (PVD), chemical vapor is deposition (CVD),or atomic layer deposition (ALD). The upper insertion layer 124 mayprevent oxidation of the upper layer by trapping external diffusion ofoxygen inside the channel layer 120 in a subsequent heat treatmentprocess, preventing resistance degradation due to metal oxidation. Theupper insertion layer 124 may be formed after forming the channel layer120.

An upper barrier layer 125 may be formed on the upper insertion layer124. The upper barrier layer 125 may be positioned between the uppercontact 130 and the upper insertion layer 124. The upper barrier layer125 may have a cylindrical shape. The diameter (or width) of the upperbarrier layer 125 may be the same as the diameter (or width) of theupper contact 130. The thickness of the upper barrier layer 125 may bethe same as or different from the thickness of the upper insertion layer124.

The upper barrier layer 125 may include a material capable of oxygenscavenging. The upper barrier layer 125 may include a metal or a metalcompound. The upper barrier layer 125 may include titanium (Ti),titanium nitride (TiN), or a combination thereof. The upper barrierlayer 125 may be formed by a method, such as chemical vapor deposition(CVD), physical vapor deposition (PVD), atomic layer deposition (ALD),plasma enhanced CVD (PECVD), and plasma enhanced ALD (PEALD).

In an embodiment, the upper barrier layer 125 capable of oxygenscavenging is formed between the channel layer 120 and the is uppercontact 130, reducing the contact resistance to the upper and lowermetal materials. Further, the upper insertion layer 124 capable oftrapping oxygen is formed under the upper barrier layer 125, gatheringoxygen ions drawn by the scavenging of the upper barrier layer 125 andhence preventing oxidation of the upper barrier layer 125 and anincrease in interfacial resistance while reducing contact resistance.

The graph of FIG. 4A illustrates a doping concentration of the metalcomponent as a function of the height position. Metallicity may increaseas the doping concentration increases. As the metallicity of the uppersurface of the channel layer 120 increases, the contact resistance tothe upper contact 130 may decrease. As the metallicity of the lowersurface of the channel layer 120 increases, the contact resistance tothe lower contact 110 may decrease. The graph of FIG. 4A may be similarto the graph of FIG. 2. Accordingly, the same reference denotations asthose in FIG. 2 may refer to the same components.

The doping concentration may be divided into a first doping region P1according to the height LB of the lower contact, a second doping regionP2 according to the height LBO of the lower channel layer, a thirddoping region P3 according to the height LG of the intermediate channellayer, a fourth doping region P4 according to the height LTO of theupper channel layer, and a fifth doping region P5 according to theheight LT of the upper contact and, unlike the graph of FIG. 2, may isfurther include a region according to the height LM1 of the upperinsertion layer 124. The doping concentration according to the heightmay be continuous.

The doping profile between the third doping region P3 and the seconddoping region P2 may include an abrupt profile, e.g., a step change. Asthe difference in doping concentration between the third doping regionP3 and the second doping region P2 increases, the difference in dopingconcentration between the second doping region P2 and the first dopingregion P1 may decrease. As the difference in doping concentrationbetween the second doping region P2 and the first doping region P1decreases, the contact resistance to the lower contact 110 may decrease.

The doping concentration of the fourth doping region P4 may increasewith a constant slope. For example, the doping concentration of thefourth doping region P4 may increase from a doping concentration equalto the doping concentration of the third doping region P3 to a dopingconcentration equal to the doping concentration of the second dopingregion P2. The fourth doping region P4 may include a gradual dopingprofile. As the fourth doping region P4 has a gradual doping profile,leakage current may be reduced.

The region according to the height LM1 of the upper insertion layer 124may include a section in which the doping concentration varies. That is,the region according to the height LM1 of the upper insertion layer 124may include both the highest doping concentration of the fourth dopingregion P4 and the doping concentration of the fifth doping region P5.The region according to the height LM1 of the upper insertion layer 124may include both a gradual doping profile and a constant doping profile.As the change in doping concentration decreases in the region accordingto the height LM1 of the upper insertion layer 124, the contactresistance to the upper contact 130 may decrease.

The fifth doping region P5 may be a region including the upper barrierlayer 125 and the upper contact 130. The doping concentration of thefifth doping region P5 may have a constant value. The dopingconcentration of the fifth doping region P5 may be lower than or equalto the doping concentration of the first doping region P1. The dopingconcentration of the fifth doping region P5 may be continuous from thedoping concentration of the fourth doping region P4.

According to the present embodiment, the contact resistance to the uppercontact 130 may be reduced by forming a high doping concentration at theupper and lower surfaces of the channel layer 120. According to thepresent embodiment, the leakage current of the vertical transistor 101may be reduced by forming a doping profile of metal component varyingaccording to the height.

As illustrated in FIG. 4B, a vertical transistor 102 may be formed. Thevertical transistor 102 may include a upper insertion layer 126 formedon the upper channel layer 123. The vertical transistor 102 s mayinclude an upper barrier layer 125 formed on the upper insertion layer126. The upper insertion layer 126 may have a rectangular column shape.The upper insertion layer 126 may have the same width as the upperchannel layer 123. The upper barrier layer 125 may cover the bottomsurface of the upper contact 130. The upper insertion layer 126 maycover the upper surface of the upper channel layer 123.

The graph of FIG. 48 may be similar to the graph of FIG. 4A.Accordingly, the same reference numerals as those in FIG. 4A may referto the same components.

As illustrated in FIG. 4C, a vertical transistor 103 may be formed. Thevertical transistor 103 may include a upper insertion layer 124 and anupper barrier layer 125, similar to the vertical transistor 101 of FIG.4A. Unlike the vertical transistor 101 of FIG. 4A, the verticaltransistor 103 may further include a lower barrier layer 127 formedbetween the lower contact 110 and the lower channel layer 121 and alower insertion layer 128 formed on the lower barrier layer 127.

The lower barrier layer 127 may have a rectangular column shape. Thewidth of the lower barrier layer 127 may be the same as the width of thelower contact 110. The lower harrier layer 127 may include the samematerial as the upper barrier layer 125. Accordingly, the lower barrierlayer 127 may include a material capable of oxygen scavenging. The lowerbarrier layer 127 may include a metal or a metal compound. The lowerbarrier layer 127 may include titanium (Ti), titanium nitride (TiN), ora combination thereof. The lower barrier layer 127 may be formed by amethod, such as chemical vapor deposition (CVD), physical vapordeposition (PVD), atomic layer deposition (ALD), plasma enhanced CVD(PECVD), and plasma enhanced ALD (PEALD).

The lower insertion layer 128 may be formed on the lower barrier layer127. The lower insertion layer 128 may have a rectangular column shape.The lower insertion layer 128 may have the same width as the lowercontact 110. The lower insertion layer 128 may overlap the upper surfaceof the lower contact 110. The lower insertion layer 128 may cover thelower surface of the lower channel layer 121. The thickness of the lowerinsertion layer 128 may be the same as or different from the thicknessof the lower barrier layer 127.

The lower insertion layer 128 may include the same material as the upperinsertion layer 124. The lower insertion layer 128 may be formed ofindium (In) or an indium-tin (InSn) compound. The lower insertion layer128 may be formed by physical vapor deposition (PVD), chemical vapordeposition (CVD), or atomic layer deposition (ALD). The lower insertionlayer 128 may prevent oxidation of the lower layer by trapping theexternal diffusion of oxygen inside the channel layer 120 in asubsequent heat treatment process, preventing resistance degradation dueto metal oxidation.

In an embodiment, the upper barrier layer 125 and the lower barrierlayer 127 capable of oxygen scavenging, are formed, respectively,between the channel layer 120 and the upper contact 130 and between thechannel layer 120 and the lower contact 110, reducing the contactresistance to the upper and lower metal materials. Further, the upperinsertion layer 124 and the lower insertion layer 128 capable oftrapping oxygen are formed under the upper barrier layer 125 and overthe lower barrier layer 127, respectively, gathering the oxygen ionsdrawn by the scavenging of the upper barrier layer 125 and the lowerbarrier layer 127 and, hence, preventing oxidation of the upper barrierlayer 125 and the lower barrier layer 127 and an increase in interfacialresistance while reducing contact resistance.

The graph of FIG. 4C illustrates the doping concentration of the metalcomponent according to the height. Metallicity may increase as thedoping concentration increases. As the metallicity of the upper surfaceof the channel layer 120 increases, the contact resistance to the uppercontact 130 may decrease. As the metallicity of the lower surface of thechannel layer 120 increases, the contact resistance to the lower contact110 may decrease. The graph of FIG. 4C may be similar to the graph ofFIG. 4A. Accordingly, the same reference numerals as those in FIG. 4Amay refer to the same components.

The doping concentration may be divided into a first doping region P1according to the height LB of the lower contact, a second doping regionP2 according to the height LBO of the lower channel layer, a thirddoping region P3 according to the height LG of the intermediate channellayer, a fourth doping region P4 according to the height LTO of theupper channel layer, and a fifth doping region P5 according to theheight LT of the upper contact and, unlike the graph of FIG. 4A, may isfurther include a region according to the height LM2 of the lowerinsertion layer 128. The doping concentration according to the heightmay be continuous.

The first doping region P1 may be a region including the lower contact110 and the lower barrier layer 127. The doping concentration of thefirst doping region P1 may have a constant value.

The region according to the height LM2 of the lower insertion layer 128may be positioned between the first doping region P1 and the seconddoping region P2. The region according to the height LM2 of the lowerinsertion layer 128 may include both the doping concentration of thefirst doping region P1 and the doping concentration of the second dopingregion P2. The region according to the height LM2 of the lower insertionlayer 128 may include a section in which the doping concentrationchanges. That is, the region according to the height LM2 of the lowerinsertion layer 128 may include a section in which the dopingconcentration changes from the doping concentration of the first dopingregion P1 to the doping concentration of the second doping region P2. Asthe change in the region according to the height LM2 of the lowerinsertion layer 128 decreases, the contact resistance to the lowercontact 110 may decrease.

The doping profile between the third doping region P3 and the seconddoping region P2 may include an abrupt profile, e.g., a step change. Asthe difference in doping concentration between the third doping regionP3 and the second doping region P2 increases, the change in dopingconcentration in the region according to the height LM2 of the lowerinsertion layer 128 may decrease.

The fourth doping region P4 may include a gradual doping profile. As thefourth doping region P4 has a gradual doping profile, leakage currentmay be reduced.

The region according to the height LM1 of the upper insertion layer 124may include a section in which the doping concentration varies. That is,the region according to the height LM1 of the upper insertion layer 124may connect the highest doping concentration in the fourth doping regionP4 and the doping concentration in the fifth doping region P5. Theregion according to the height LM1 of the upper insertion layer 124 mayinclude both a gradual doping profile and a constant doping profile. Asthe change in doping concentration decreases in the region according tothe height LM1 of the upper insertion layer 124, the contact resistanceto the upper contact 130 may decrease.

The fifth doping region P5 may be a region including the upper barrierlayer 125 and the upper contact 130. The doping concentration of thefifth doping region P5 may have a constant value.

According to the present embodiment, the contact resistance to the lowercontact 110 and the upper contact 130 may be reduced by forming a higherdoping concentration at the upper and lower surfaces of the channellayer 120. According to the present embodiment, the leakage current ofthe vertical transistor 103 may be is reduced by varying the dopingprofile of impurities according to the height.

As illustrated in FIG. 4D, a vertical transistor 104 may be formed. Thevertical transistor 104 may include a upper insertion layer 126 and anupper barrier layer 125, similar to the vertical transistor 102 of FIG.4B. Unlike the vertical transistor 102 of FIG. 4B, the verticaltransistor 104 has a lower barrier layer 127 between the lower contact110 and the lower channel layer 121 and a lower insertion layer 128 onthe lower barrier layer 127. The lower barrier layer 127 and the lowerinsertion layer 128 of the vertical transistor 104 may be the same asthe vertical transistor 103 of FIG. 4C.

The graph of FIG. 4D may be similar to the graph of FIG. 4C.Accordingly, the same reference denotations as those in FIG. 4C mayrefer to the same components.

FIG. 5 is a view illustrating a vertical transistor 200 according toanother embodiment. The vertical transistor 200 may be similar to thevertical transistor 100 of FIG. 1. The vertical transistor 200 may besimilar to the vertical transistor 100 of FIG. 1 except for the shape ofthe components. Accordingly, the materials included in the components ofthe vertical transistor 200 may be the same or similar to the materialsincluded in the components of the vertical transistor 100 of FIG. 1.

The vertical transistor 200 may include a cylindrical lower contact 210,a channel layer 220 formed on the lower contact 210, and an uppercontact 230 formed on the channel layer 220. The lower contact 210, thechannel layer 220, and the upper contact 23 may all have a cylindricalshape. The lower contact 210, the channel layer 220, and the uppercontact 23 may have the same diameter (also referred to as width). Adielectric layer 240 may be formed on the channel layer 220. Thedielectric layer 240 may cover the channel layer 220. The gate 250 maybe formed to surround the dielectric layer 240. The thickness of thegate 250 may be larger than the thickness of the dielectric layer 240.The gate 250 may cover the channel layer 220. Accordingly, thedielectric layer 240 may be positioned between the gate 250 and thechannel layer 220.

FIG. 6 is a view in which the dielectric layer 240 and the gate 250 ofFIG. 5 are omitted to describe the channel layer 220 of FIG. 5.

As illustrated in FIG. 6, the channel layer 220 may include a lowerchannel layer 221 on the lower contact 120, an intermediate channellayer 222 on the lower channel layer 221, and an upper channel layer 223on the intermediate channel layer 222. That is, the channel layer 220may include a stack of the lower channel layer 221, the intermediatechannel layer 222, and the upper channel layer 223. The height LBO ofthe lower channel layer 221, the height LG of the intermediate channellayer 222, and the height LTO of the upper channel layer 223 may be thesame or different.

The channel layer 220 may include an oxide. The channel layer 220 mayinclude a metal material and an oxygen material. The channel layer 220may be doped with an impurity. The channel layer 220 may include anoxide semiconductor. The channel layer 220 may have a non-uniform dopingprofile according to the height. The doping profile of impurities may bedifferent in the lower channel layer 221, the intermediate channel layer222, and the upper channel layer 223.

The graph of FIG. 6 illustrates the doping concentration of the metalcomponent according to the height. Metallicity may increase as thedoping concentration increases. As the metallicity of the upper surfaceof the channel layer 220 increases, the contact resistance to the uppercontact 230 may decrease. As the metallicity of the lower surface of thechannel layer 220 increases, the contact resistance to the lower contact210 may decrease.

The doping concentration may be divided into a first doping region P1according to the height LB of the lower contact, a second doping regionP2 according to the height LBO of the lower channel layer, a thirddoping region P3 according to the height LG of the intermediate channellayer, a fourth doping region P4 according to the height LTO of theupper channel layer, and a fifth doping region P5 according to theheight LT of the upper contact. The doping concentration of the first tofifth doping regions P1 to P5 may be continuous.

First, the doping concentrations of the first doping region P1, thesecond doping region P2, and the third doping region P3 may each includea constant value. The doping profiles of the first doping region P1, thesecond doping region P2, and the third doping region P3 may include astepped profile. The doping concentration of the first doping region P1may be greater than the doping concentration of the second doping regionP2 and the third doping region P3. The doping concentration of thesecond doping region P2 may be greater than the doping concentration ofthe third doping region P3. The third doping region P3 may include thelowest doping concentration among the first to fifth doping regions P1to P5. The difference in doping concentration between the second dopingregion P2 and the third doping region P3 may be greater than thedifference in doping concentration between the first doping region P1and the second doping region P2. The difference in doping concentrationbetween the second doping region P2 and the third doping region P3 maybe at least two times greater than the difference in dopingconcentration between the first doping region P1 and the second dopingregion P2. That is, the doping profile between the third doping regionP3 and the second doping region P2 may include an abrupt profile, e.g.,a step change. As the difference in doping concentration between thethird doping region P3 and the second doping region P2 increases, thedifference in doping concentration between the second doping region P2and the first doping region P1 may decrease. As the difference in dopingconcentration between the second doping region P2 and the first dopingregion P1 decreases, the contact resistance to the lower contact 210 maydecrease.

The doping concentration of the fourth doping region P4 may increasewith a constant slope. The doping concentration of the fourth dopingregion P4 may increase from a doping concentration equal to the dopingconcentration of the third doping region P3 to a doping concentrationequal to the doping concentration of the fifth doping region P5. Thedoping concentration of the fourth doping region P4 may increase from adoping concentration equal to the doping concentration of the thirddoping region P3 to a doping concentration equal to the dopingconcentration of the second doping region P2. That is, the fourth dopingregion P4 may include a gradual doping profile. In another embodiment,the doping profile of the fourth doping region P4 may increase as theslope of the doping concentration according to the height increases. Inanother embodiment, the doping profile of the fourth doping region P4may increase as the slope decreases. As the fourth doping region P4 hasa gradual doping profile, leakage current may be reduced. As thedifference in doping concentration between the fourth doping region P4and the fifth doping region P5 decreases, the contact resistance to theupper contact 230 may decrease.

The doping concentration of the fifth doping region P5 may have aconstant value. The doping concentration of the fifth doping region P5may be lower than or equal to the doping concentration of the firstdoping region P1. The doping concentration of the fifth doping region P5may be continuous from the doping concentration of the fourth dopingregion P4.

According to the present embodiment, the leakage current of the verticaltransistor 200 may be reduced by varying the doping profile ofimpurities according to the height.

According to the present embodiment, the contact resistance to the lowercontact 210 and the upper contact 230 may be reduced by forming a higherdoping concentration at the upper and lower surfaces of the channellayer 220.

FIGS. 7A to 7B are perspective views illustrating example verticaltransistors. FIGS. 7A to 7B are views in which the dielectric layer 240and the gate 250 of FIG. 5 are omitted to describe the lower contact210, the channel layer 220, and the upper contact 230 according tovarious embodiments. Accordingly, the vertical transistors 201 and 202of FIGS. 7A to 7B may be similar to each other. The vertical transistors201 and 202 of FIGS. 7A to 7B may be similar to the vertical transistor200 of FIG. 6. Accordingly, the same reference denotations as those inFIG. 6 among the reference denotations of FIGS. 7A to 7B may refer tothe same components.

First, as illustrated in FIG. 7A, a vertical transistor 201 may beformed. The vertical transistor 201 may include a upper insertion layer224 formed on the upper channel layer 223.

The upper insertion layer 224 may have a cylindrical shape. The upperinsertion layer 224 may have the same diameter (or width) as the uppercontact 230. The upper insertion layer 224 may overlap the lower surfaceof the upper contact 230. The upper insertion layer 224 may partiallycover the upper surface of the upper channel layer 223.

The upper insertion layer 224 may be formed of an indium (In) or anindium-tin (InSn) compound. The upper insertion layer 224 may be formedby physical vapor deposition (PVD), chemical vapor deposition (CVD), oratomic layer deposition (ALD). The upper insertion layer 224 may preventoxidation of the upper layer by trapping external diffusion of oxygeninside the channel layer 220 in a subsequent heat treatment process,preventing resistance degradation due to metal oxidation. The upperinsertion layer 224 may be formed after forming the channel layer 220.

An upper barrier layer 225 may be formed on the upper insertion layer224. The upper barrier layer 225 may be positioned between the uppercontact 230 and the upper insertion layer 224. The upper barrier layer225 may have a cylindrical shape. The width of the upper barrier layer225 may be the same as the width of the upper contact 230. The thicknessof the upper barrier layer 225 may be the same as or different from thethickness of the upper insertion layer 224.

The upper barrier layer 225 may include a material capable of oxygenscavenging. The upper barrier layer 225 may include a metal or a metalcompound. The upper barrier layer 225 may include titanium (Ti),titanium nitride (TIN), or a combination thereof. The upper barrierlayer 225 may be formed by a method, such as chemical vapor deposition(CVD), physical vapor deposition (PVD), atomic layer is deposition(ALD), plasma enhanced CVD (PECVD), and plasma enhanced ALD (PEALD).

In an embodiment, the upper barrier layer 225 capable of oxygenscavenging is formed between the channel layer 220 and the upper contact230, reducing the contact resistance to the upper and lower metalmaterials. Further, the upper insertion layer 224 capable of trappingoxygen is formed under the upper barrier layer 225, gathering oxygenions drawn by the scavenging of the upper barrier layer 225 and hencepreventing oxidation of the upper barrier layer 224 and an increase ininterfacial resistance while reducing contact resistance.

The graph of FIG. 7A illustrates the doping concentration of the metalcomponent according to the height. Metallicity may increase as thedoping concentration increases. As the metallicity of the upper surfaceof the channel layer 220 increases, the contact resistance to the uppercontact 230 may decrease. As the metallicity of the lower surface of thechannel layer 220 increases, the contact resistance to the lower contact210 may decrease. The graph of FIG. 7A may be similar to the graph ofFIG. 6. Accordingly, the same reference denotations as those in FIG. 6may refer to the same components. Description of duplicate componentswill be omitted.

The doping concentration may be divided into a first doping region P1according to the height LB of the lower contact, a second doping regionP2 according to the height LBO of the lower channel layer, is a thirddoping region P3 according to the height LG of the intermediate channellayer, a fourth doping region P4 according to the height LTO of theupper channel layer, and a fifth doping region P5 according to theheight LT of the upper contact and, unlike the graph of FIG. 6, mayfurther include a region according to the height LM1 of the upperinsertion layer 224. The doping concentration according to the heightmay be continuous.

The doping profile between the third doping region P3 and the seconddoping region P2 may include an abrupt profile, e.g., a step change. Asthe difference in doping concentration between the third doping regionP3 and the second doping region P2 increases, the difference in dopingconcentration between the second doping region P2 and the first dopingregion P1 may decrease. As the difference in doping concentrationbetween the second doping region P2 and the first doping region P1decreases, the contact resistance to the lower contact 210 may decrease.

The doping concentration of the fourth doping region P4 may increasewith a constant slope. For example, the doping concentration of thefourth doping region P4 may increase from a doping concentration equalto the doping concentration of the third doping region P3 to a dopingconcentration equal to the doping concentration of the second dopingregion P2. The fourth doping region P4 may include a gradual dopingprofile. As the fourth doping region P4 has a gradual doping profile,leakage current may be reduced.

The region according to the height LM1 of the upper insertion layer 224may include a section in which the doping concentration varies. That is,the region according to the height LM1 of the upper insertion layer 224may connect the highest doping concentration in the fourth doping regionP4 and the doping concentration in the fifth doping region P5. Theregion according to the height LM1 of the upper insertion layer 224 mayinclude both a gradual doping profile and a constant doping profile. Asthe change in doping concentration decreases in the region according tothe height LM1 of the upper insertion layer 224, the contact resistanceto the upper contact 230 may decrease.

The fifth doping region P5 may be a region including the upper barrierlayer 225 and the upper contact 230. The doping concentration of thefifth doping region P5 may have a constant value. The dopingconcentration of the fifth doping region P5 may be lower than or equalto the doping concentration of the first doping region P1. The dopingconcentration of the fifth doping region P5 may be continuous from thedoping concentration of the fourth doping region P4.

According to the present embodiment, the contact resistance to the uppercontact 230 may be reduced by increasing the doping concentration of theupper surface of the channel layer 220. According to the presentembodiment, the leakage current of the vertical transistor 201 may bereduced by forming a doping profile of impurities varying according tothe height.

As illustrated in FIG. 7B, a vertical transistor 202 may be formed. Thevertical transistor 202 may include a upper insertion layer 224 and anupper barrier layer 225, similar to the vertical transistor 201 of FIG.7A. Unlike the vertical transistor 201 of FIG. 7A, the verticaltransistor 202 may further include a lower barrier layer 226 between thelower contact 210 and the lower channel layer 221 and a lower insertionlayer 227 on the lower barrier layer 226.

The lower barrier layer 226 may have a cylindrical shape. The diameterof the lower barrier layer 226 may be the same as the diameter of thelower contact 210. The lower barrier layer 226 may include the samematerial as the upper barrier layer 225. Accordingly, the lower barrierlayer 226 may include a material capable of oxygen scavenging. The lowerbarrier layer 226 may include a metal or a metal compound. The lowerbarrier layer 226 may include titanium (Ti), titanium nitride (TiN), ora combination thereof. The lower barrier layer 226 may be formed by amethod, such as chemical vapor deposition (CVD), physical vapordeposition (PVD), atomic layer deposition (ALD), plasma enhanced CVD(PECVD), and plasma enhanced ALD (PEALD).

The lower insertion layer 227 may be formed on the lower barrier layer226. The lower insertion layer 227 may have a cylindrical shape. Thelower insertion layer 227 may have the same diameter (or width) as thelower contact 210. The lower barrier layer 226 may cover the uppersurface of the lower contact 210. The lower insertion layer 227 maycover the lower surface of the lower channel layer 221. The thickness ofthe lower insertion layer 227 may be the same as or different from thethickness of the lower barrier layer 226.

The lower insertion layer 227 may include the same material as the upperinsertion layer 224. The lower insertion layer 227 may be formed ofindium (In) or an indium-tin (InSn) compound. The lower insertion layer227 may be formed by physical vapor deposition (PVD), chemical vapordeposition (CVD), or atomic layer deposition (ALD). The lower insertionlayer 227 may prevent oxidation of the lower layer by trapping theexternal diffusion of oxygen inside the channel layer 220 in asubsequent heat treatment process, preventing resistance degradation dueto metal oxidation.

In an embodiment, the upper barrier layer 225 and the lower barrierlayer 226 capable of oxygen scavenging, respectively, are formed betweenthe channel layer 220 and the upper contact 230 and between the channellayer 220 and the lower contact 210, for reducing the contact resistanceto the upper and lower metal materials. Further, the upper insertionlayer 224 and the lower insertion layer 227 capable of trapping oxygenare formed under the upper barrier layer 225 and over the lower barrierlayer 226, respectively, gathering the oxygen ions drawn by thescavenging of the upper barrier layer 225 and the lower barrier layer226 and hence preventing oxidation of the upper barrier layer 225 andthe lower barrier layer 226 and an increase in interfacial resistancewhile reducing contact resistance.

The graph of FIG. 76 illustrates the doping concentration of the metalcomponent according to the height. Metallicity may increase as thedoping concentration increases. As the metallicity of the upper surfaceof the channel layer 220 increases, the contact resistance to the uppercontact 230 may decrease. As the metallicity of the lower surface of thechannel layer 220 increases, the contact resistance to the lower contact210 may decrease. The graph of FIG. 7B may be similar to the graph ofFIG. 7A. Accordingly, the same reference numerals as those in FIG. 7Amay refer to the same components. Description of duplicate components aill be omitted.

The doping concentration may be divided into a first doping region P1according to the height LB of the lower contact, a second doping regionP2 according to the height LBO of the lower channel layer, a thirddoping region P3 according to the height LG of the intermediate channellayer, a fourth doping region P4 according to the height LTO of theupper channel layer, and a fifth doping region P5 according to theheight LT of the upper contact and, unlike the graph of FIG. 7A, mayfurther include a region according to the height LM2 of the lowerinsertion layer 227. The doping concentration according to the heightmay be continuous.

The first doping region P1 may be a region including the lower contact210 and the lower barrier layer 226. The doping concentration of thefirst doping region P1 may have a constant value.

The region according to the height LM2 of the lower insertion layer 227may be positioned between the first doping region P1 and the seconddoping region P2. The region according to the height LM2 of the lowerinsertion layer 227 may include both the doping concentration of thefirst doping region P1 and the doping concentration of the second dopingregion P2. The region according to the height LM2 of the lower insertionlayer 227 may include a section in which the doping concentrationchanges. That is, the region according to the height LM2 of the lowerinsertion layer 227 may include a section in which the dopingconcentration changes from the doping concentration of the first dopingregion Pt to the doping concentration of the second doping region P2. Asthe change in the region according to the height LM2 of the lowerinsertion layer 227 decreases, the contact resistance to the lowercontact 210 may decrease.

The doping profile between the third doping region P3 and the seconddoping region P2 may include an abrupt profile, e.g., a step change. Asthe difference in doping concentration between the third doping regionP3 and the second doping region P2 increases, the change in dopingconcentration in the region according to the height LM2 of the lowerinsertion layer 227 may decrease.

The fourth doping region P4 may include a gradual doping profile. As thefourth doping region P4 has a gradual doping profile, leakage currentmay be reduced.

The region according to the height LM1 of the upper insertion layer 224may include a section in which the doping concentration varies. That is,the region according to the height LM1 of the upper insertion layer 224may connect the highest doping concentration in the fourth doping regionP4 and the doping concentration in the fifth doping region P5. Theregion according to the height LM1 of the upper insertion layer 224 mayinclude both a gradual doping profile and a constant doping profile. Asthe change in doping concentration decreases in the region according tothe height LM1 of the upper insertion layer 224, the contact resistanceto the upper contact 230 may decrease.

The fifth doping region P5 may be a region including the upper barrierlayer 225 and the upper contact 230. The doping concentration of thefifth doping region P5 may have a constant value.

According to the present embodiment, the contact resistance to the lowercontact 210 and the upper contact 230 may be reduced by forming a higherdoping concentration at the upper and lower surfaces of the channellayer 220. According to the present embodiment, the leakage current ofthe vertical transistor 202 may be reduced by forming a doping profileof impurities varying according to the height.

FIG. 8 is a perspective view illustrating a variation to the verticaltransistor of FIG. 1. The vertical transistor 300 of FIG. 8 may besimilar to the vertical transistor 100 of FIG. 1. Accordingly, the samereference denotations as those in FIG. 1 may refer to the samecomponents. The vertical transistor 300 of FIG. 8 may have a similar isstructure to the vertical transistor 100 of FIG. 1 except for thedielectric layer 141 and the gate 151. Accordingly, to avoid redundancy,descriptions of components already described above will be omittedherein.

As illustrated in FIG. 8, the gate 151 may cover a pair of oppositesidewalls of the channel layer 120. A pair of parallel gates 151 may beformed. A dielectric layer 141 may be formed between the gate 151 andthe channel layer 120. Accordingly, a pair of parallel dielectric layers141 may be formed on a pair of opposite sidewalls of the channel layer120. The dielectric layer 141 and the gate 151 may include the samematerial as the dielectric layer 140 and the gate 150 of FIG. 1.

Although not shown, the vertical transistor 300 of FIG. 8 may include alower barrier layer, a lower insertion layer, a upper insertion layer,and an upper barrier layer as illustrated in FIGS. 4A to 4C. Thevertical transistor 300 of FIG. 8 may include a cylindrical lowerelectrode and channel layer as illustrated in FIG. 5, and may include alower barrier layer, a lower insertion layer, a upper insertion layer,and an upper barrier layer as illustrated in FIGS. 7A to 7B.

While the disclosure has been shown and described in relation toembodiments thereof, it will be readily appreciated by one of ordinaryskill in the art that various changes or modifications may be madethereto without departing from the technical spirit of the disclosure.

What is claimed is:
 1. A semiconductor device, comprising: a lowercontact; s a vertical channel layer on the lower contact, the verticalchannel layer including a metal component and an oxygen component; andan upper contact on the vertical channel layer, wherein the verticalchannel layer has a gradual doping profile in which a dopingconcentration of the metal component is lowest in an intermediate regionand gradually increases from the intermediate region to the uppercontact.
 2. The semiconductor device of claim 1, wherein the verticalchannel layer further has an abrupt doping profile in which the dopingconcentration of the metal component remains constant in a predeterminedheight from the intermediate region and sharply increases in a regioncloser to the lower contact.
 3. The semiconductor device of claim 1,wherein the vertical channel layer includes at least any one of oxygen(O), indium (In), gallium (Ga), or zinc (Zn).
 4. The semiconductordevice of claim 1, wherein the vertical channel layer is doped with animpurity.
 5. The semiconductor device of claim 4, wherein the impurityincludes silicon (Si) or germanium (Ge).
 6. The semiconductor device ofclaim 1, further comprising: a upper insertion layer on the verticalchannel layer; and an upper barrier layer between the upper insertionlayer and the upper contact.
 7. The semiconductor device of claim 6,wherein the upper insertion layer includes indium or an indium-tincompound, and wherein the upper barrier layer includes titanium (Ti) ortitanium nitride (TiN).
 8. The semiconductor device of claim 6, furthercomprising: a lower barrier layer on the lower contact; and a lowerinsertion layer between the lower barrier layer and the vertical channellayer.
 9. The semiconductor device of claim 8, wherein the lowerinsertion layer includes the same material as the upper insertion layer,and wherein the lower barrier layer includes the same material as theupper barrier layer.
 10. The semiconductor device of claim 1, whereinthe vertical channel layer further includes a gate covering an exposedsidewall of the vertical channel layer, and a dielectric layer betweenthe gate and the vertical channel layer.
 11. A vertical transistor,comprising: a lower contact on a substrate; a channel layer including alower channel layer, an intermediate channel layer, and an upper channellayer sequentially formed on the lower contact, the channel layerincluding a metal component and an oxygen component; and an uppercontact on the upper channel layer, wherein the channel layer has agradual doping profile in which a doping concentration of the metalcomponent is lowest in the intermediate channel layer and, in the upperchannel layer, gradually increases towards the upper contact.
 12. Thevertical transistor of claim 11, wherein the channel layer has an abruptdoping profile in which the doping concentration of the metal componentsharply increases at a boundary between the intermediate channel layerand the lower channel layer.
 13. The vertical transistor of claim 11,wherein the doping concentration of the metal component remains constantin the intermediate channel layer and the lower channel layer.
 14. Thevertical transistor of claim 11, wherein the channel layer includes atleast any one of oxygen (O), indium (In), gallium (Ga), or zinc (Zn).15. The vertical transistor of claim 11, wherein the channel layer isdoped with an impurity.
 16. The vertical transistor of claim 15, whereinthe impurity includes silicon (Si) or germanium (Ge).
 17. The verticaltransistor of claim 11, wherein the lower channel layer is formed in alow-concentration oxygen atmosphere, and the intermediate channel layerand the upper channel layer are formed in a high-concentration oxygenatmosphere.
 18. The vertical transistor of claim 11, wherein the upperchannel layer has a constant doping concentration of the metal componentat a surface of the upper channel layer, and wherein the dopingconcentration of the metal component at the surface of the upper channellayer is the same as that of the upper contact.
 19. The verticaltransistor of claim 11, further comprising: a upper insertion layer onthe upper channel layer; and an upper barrier layer between the upperinsertion layer and the upper contact.
 20. The vertical transistor ofclaim 19, wherein the upper insertion layer includes indium or anindium-tin compound, and wherein the upper barrier layer includestitanium (Ti) or titanium nitride.
 21. The vertical transistor of claim19, further comprising: a lower barrier layer on the lower contact; anda lower insertion layer between the lower barrier layer and the lowerchannel layer.
 22. The vertical transistor of claim 21, wherein thelower insertion layer includes the same material as the upper insertionlayer, and wherein the lower barrier layer includes the same material asthe upper barrier layer.
 23. A method for manufacturing a verticaltransistor, the method comprising: forming a lower contact material on asubstrate; forming a lower channel material including a metal componentand an oxygen component on the lower contact material; forming a channelmaterial including a metal component and an oxygen component on thelower channel material; and performing a treatment on the channelmaterial to separate the channel material into an intermediate channelmaterial and an upper channel material on the intermediate channelmaterial.
 24. The method of claim 23, wherein the lower channel materialis formed in a low-concentration oxygen atmosphere, and the channelmaterial is formed in a high-concentration oxygen atmosphere.
 25. Themethod of claim 23, wherein the lower channel material and the channelmaterial are formed in-situ or ex-situ.
 26. The method of claim 23,wherein the treatment uses plasma.
 27. The method of claim 23, whereinthe treatment uses an inert gas.
 28. The method of claim 23, wherein thelower channel material and the channel material include at least any oneof oxygen (O), indium (in), gallium (Ga), or zinc (Zn).
 29. The methodof claim 23, wherein the lower channel material and the channel materialare doped with an impurity.
 30. The method of claim 29, wherein theimpurity includes silicon (Si) or germanium (Ge).
 31. The method ofclaim 23, wherein a boundary between the intermediate channel materialand the lower channel material has an abrupt doping profile in which adoping concentration of the metal component sharply increases, andwherein the upper channel material has a gradual doping profile in whichthe doping concentration of the metal component gradually increasestowards an upper surface of the upper channel material.
 32. The methodof claim 23, further comprising: after performing the treatment, forminga lower contact, a lower channel layer, an intermediate channel layer,and an upper channel layer by etching the lower contact material, thelower channel material, the intermediate channel material, and the upperchannel material; forming a upper insertion layer on the upper channellayer; and forming an upper barrier layer on the upper insertion layer,wherein the upper insertion layer includes indium or an indium-tincompound.
 33. The method of claim 23, further comprising: afterperforming the treatment, forming a lower contact, a lower channellayer, an intermediate channel layer, and an upper channel layer byetching the lower contact material, the lower channel material, theintermediate channel material, and the upper channel material; formingan upper barrier layer on the upper channel layer; forming an uppercontact on the upper barrier layer; and forming a upper insertion layerbetween the upper channel layer and the upper barrier layer, wherein theupper insertion layer includes indium or an indium-tin compound.